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The Indiana Department of Transportation (INDOT) commissioned the construction of six bridge decks utilizing a new class of internally cured high performance concrete (IC HPC). The first four bridge decks were constructed in the summer of 2013, while the fifth was built in November of 2014 and the sixth is planned for the summer of 2015. These decks implement research findings presented in the FHWA/IN/JTRP-2010/10 report (Schlitter, Henkensiefken, et al. 2010) where internal curing was proposed as one method to reduce the potential for shrinkage cracking, leading to improved durability. In addition, the use of higher performance concrete mixtures and a new specification composed of prescriptive and performance based measures was implemented with the intention of extending the service life of the bridge decks. The objectives of this thesis are to provide documentation of the construction and performance of the IC HPC bridge decks cast in Indiana and provide a viable, practice-ready method for the assessment of the potential durability of these concretes. In fulfillment of these objectives, samples of the IC HPC used in construction were compared to a reference high performance concrete (HPC) which did not utilize internal curing and was made by the same producer with the same constituent materials. The samples collected in the field were transported to the laboratory where the mechanical performance, resistance to chloride ingress, and potential for shrinkage and cracking was assessed. Using experimental results and mixture proportions, the diffusion based service life of the bridge decks was able to be estimated. The construction process was documented for first four bridge decks made using internal cured high performance concrete (IC HPC). These concretes were able to be designed, batched, and placed and are now in service. While avoidable issues were observed during batching construction related to corrections of batching water, batching tolerances and fluctuations in air content (which apply to any concrete), the IC HPC was able to be batched and placed using slight modifications to conventional methods. The production of the IC HPC mixtures was implemented using a mixed specification using prescriptive and performance based measures representing an improvement on previous specifications which did not specifically have provisions that consider durability. To aid in the implementation of internal curing in the field, a new quality control technique for lightweight aggregate utilizing a centrifuge has been implemented is now standardized in Indiana Testing Method 222 (Miller, Barrett, et al. 2014). The results of laboratory testing indicate that the compressive strength, modulus of elasticity, and tensile strength of the IC HPC mixtures was not substantially different than the HPC mixtures and as such current codified equations are able to be used to predict the modulus of elasticity and tensile strength if the compressive strength is known. The diffusion of chlorides in these concretes was assessed, where it was shown that each of the mixtures tested had a charge passed in the rapid chloride permeability test of less than 1500 C at 91 days (AASHTO T277-07 2007); additional testing provided equivalent results when performing the Nordtest (NT Build 492 1999), Stadium migration test , or electrical resistivity test. Using experimental results which determined the chloride diffusion and permeability, the diffusion based service life of the IC HPC bridge decks was estimated to be between approximately 60 to 90 years, compared to approximately 18 years for the conventional class C bridge deck concrete used in Indiana. The susceptibility to early age shrinkage and cracking was evaluated where it was shown that IC HPC concretes exhibited a reduction in early age shrinkage of 70 to 90%, resulting in a reduction in residual stresses of 80% or more while reducing thermally induced stress by up to 55% when compared to HPC mixtures. Collectively, these results indicate that the IC HPC mixtures that were produced as a part of this study exhibit the potential of for substantially increased service life while markedly reducing the potential for early age cracking. The second phase of this thesis investigated the role of initial sample conditioning and the effect of changes in degree of saturation on the measured electrical resistivity, where a new function was developed to describe this relationship in air entrained concretes. The consistency and variability in the determination of the chloride diffusion coefficient was investigated through standardized testing methods, where it was shown that the coefficient of variation associated with the accelerated tests was approximately 15% or less and are dependent on the test. Chloride profile measurements made on cores taken from samples which were exposed with a known deicing solution and the temperature fluctuations of West Lafayette, Indiana indicated that on average, the coefficient of variation for determining the apparent chloride diffusion coefficient under is 30% or less. In addition, the use of resistivity measurements on sealed samples was used to evaluate the variability of the concrete produced throughout the construction of the fifth IC HPC bridge deck while comparisons of the samples from the first four bridge decks produced in the laboratory and in the field were also made. The results indicated that the coefficient of variation associated with the resistivity measurements made on the fifth bridge deck was less than 5%, while experimental results indicated that industrial production consistently results in lower performance as measured by the resistivity test when compared to laboratory production. In this study it was also shown that measurements of mechanical properties are not indicative of the potential durability of the concrete. The conclusions of this thesis and the findings presented in the FHWA/IN/JTRP-2010/10 report (Schlitter, Henkensiefken, et al. 2010) and the CDOT-2014-3 report (Jones et al. 2014) indicate that internal curing is a practice-ready, engineered solution that may lead to the production of higher performance concretes which have a reduced potential for cracking. To aid in the implementation of internal curing in practice, spreadsheets which automate calculations necessary for quality control for lightweight aggregates, mixture proportioning, and moisture adjustments have been developed by Miller (2014) and have been made available with the report documenting the construction of the first four bridge decks (Barrett et al. 2015). This thesis also provided the framework for a durability based design approach using sealed electrical resistivity measurements which may be implemented in practice. This method has been shown to be a viable way to rapidly evaluate the chloride diffusion coefficient of concrete and is appropriate for testing large numbers of samples during construction. It is recommended that the approach outlined in this work be implemented in performance based specifications in lieu of other accelerated testing methods which define the performance of the concrete based on the result of that test. Finally, it should be emphasized that the implementation of technologies such as those that are presented in this thesis alone does not guarantee higher performance, as the production of such concrete requires a degree of technical competence in design, production, and construction of concrete materials. As is the case with the production of any concrete, internally cured or not, performance will be directly tied to the careful accounting of water, be it on the surface of aggregates, in the mixing drum after washing, or elsewhere. Special attention should be paid to the proper operation of batching systems, while placement techniques should be reviewed to minimize unwanted effects, and proper finishing and curing techniques must always be practiced. Only after performing the basics of concrete production properly will the full benefits of internal curing be actualized.
The project presented in this report aimed to develop an effective methodology to use saturated lightweight sand (LWS) for internal curing to enhance concrete performance and prolong service life of concrete structures. High-performance concrete (HPC) mixtures approved by MoDOT for pavement and bridge deck structures were used for the baseline mixtures. Five different types of saturated LWS employed at various contents were investigated to evaluate the optimum dosage of LWS and maximize its effectiveness on enhancing concrete performance. The content of LWS was varied to ensure the introduction of internal curing water that can secure up to 150% of the water consumed by chemical shrinkage during cement hydration (As per ASTM C1761). Performance improvement from the LWS focused mainly on reducing autogenous and drying shrinkage and the resulting cracking potential without sacrificing durability and cost competence. Proper combinations of internal and external curing were found to enhance shrinkage mitigation. Under 7 days of initial moisture curing, HPC made with the LWS3 resulted in the lowest overall shrinkage. The Bridge-LWS2-150% exhibited the best performance in mitigating autogenous shrinkage where the concrete maintained 160 micro-strain of expansion even after 175 days of age. The lowest drying shrinkage was obtained with the Bridge-LWS3-50% mixture (340 micro-strain) at 175 days subjected to 28 days of moist curing. For the paving HPC, the lowest drying shrinkage at 155 days was obtained with the Paving-LWS3-150% mixture (265 micro-strain) subjected to 28 days of moist curing. Concrete proportioned with the LWS2 expanded shale LWS exhibited the best compressive strength, regardless of the curing regime. In terms of initial moisture curing duration, the application of 7 days of moisture curing resulted in the highest compressive strength compared with other curing conditions. The 56-day compressive strength of HPC designated for bridge deck construction that was made with the LWS1 was up to 10 MPa (1,450 psi) greater than the Bridge-Reference concrete made without any LWS. The Bridge-LWS2-100% and Bridge-LWS1-50% mixtures exhibited the highest 56-day MOE of 42.5 GPa (6,615 ksi) under Standard curing. The Bridge-LWS3-100% mixture cured under Standard conditions had the highest 56-day flexural strength of 5.5 MPa (800 psi). The mixtures made with LWS2 presented the lowest sorptivity, regardless of the curing condition and LWS content. The findings from this comprehensive project provided a basis for: (1) new mixture design methodology and guidelines for using LWS for internal curing for bridge deck and pavement applications; and (2) validation of performance improvement when using internal curing and cost competitiveness in the State of Missouri.
Curing is one of those activities that every civil engineer and construction worker has heard of, but in reality does not worry about much. In practice, curing is often low on the list of priorities on the construction site, particularly when budgets and timelines are under pressure. Yet the increasing demands being placed on concrete mixtures also mean that they are less forgiving than in the past. Therefore, any activity that will help improve hydration and so performance, while reducing the risk of cracking, is becoming more important. Curing Concrete explains exactly why curing is so important and shows you how to best do it. The book covers: The fundamentals behind hydration How curing affects the properties of concrete, improving its long-term performance What curing technologies and techniques you can use for different applications How to effectively specify, provide, and measure curing in a project The author also gives numerous examples of how curing—or a lack of it—has affected concrete performance in real-world situations. These include examples from hot and cold climates, as well as examples related to high-performance concrete, performance parameters, and specifications and testing. Written for construction professionals who want to ensure the quality and longevity of their concrete structures, this book demonstrates that curing is well worth the effort and cost.
Environmental exposure is one of the primary causes of concrete pavement deterioration, specifically cyclic freezing and thawing, as is common in Kansas. Rehabilitation of deteriorated concrete pavement is a common pavement life-extension strategy, and a variety of rehabilitation techniques are often utilized depending on the level of pavement distress. Budgetary constraints, however, often dictate use of partial and full-depth patching methods to rehabilitate deteriorated concrete pavement rather than replace an entire road. For roadways with high traffic volume, patching is often done overnight within few hours. These repairs include removing the old concrete and preparing the location for new concrete, which must achieve at least 1,800 psi compressive strength 6 hours prior to opening to traffic to avoid compromising future durability. Current patches last less than 10 years despite a nominal 20-year service life. This study utilized an internal curing technique to produce durable high early strength concrete for patching. Because desorbing water throughout the concrete matrix improves the microstructure and reduces porosity, lightweight aggregates and crushed concrete aggregates were each used to desorb water and provide internal curing. Tests were conducted to evaluate compressive strength, autogenous shrinkage, length change, and freezing and thawing related to mass change, length change, and relative dynamic modulus of elasticity (RDME). In contrast to ASTM C157, which only measures drying shrinkage after 14 days of curing, autogenous shrinkage of concrete was measured in this study. KTMR-22, developed by the Kansas Department of Transportation, was used to evaluate freeze-thaw durability of internally cured repair mixtures because this method subjects test specimens to a much harsher test regimen than ASTM C666. For example, KTMR-22 utilizes 660 cycles that simulate 20 years of exposure to 33 cycles of freezing and thawing compared to ASTM-666 exposure of only 300 cycles. Results showed that the mixture made with lightweight aggregate and low cement content met all requirements for expansion and RDME. This mixture also had minimum autogenous shrinkage among all the mixtures.
Internally cured concrete has been rapidly emerging over the last decade as an effective way to improve the performance of concrete. Internal curing (IC) holds promise for producing concrete with an increased resistance to early-age cracking and enhanced durability. It is a simple and effective way to cure concrete.
Whilst most structures made using concrete and cement-based composites have not shown signs of premature degradation, there have been notable exceptions. In addition, there is increasing pressure for new structures to remain in serviceable condition for long periods with only minimal maintenance before being recycled. All these factors have highlighted the issues of what affects the durability of these materials in different circumstances and how material properties can be measured and improved. Durability of concrete and cement composites summarises key research on these important topics. After an introductory chapter, the book reviews the pore structure and chemistry of cement-based materials, providing the foundation for understanding the particular aspects of degradation which are discussed in the following chapters. These include dimensional stability and cracking processes, chemical and microbiological degradation of concrete, corrosion of reinforcing and prestressing steels, deterioration associated with certain aggregates, effects of frost and problems involving fibre-reinforced and polymer-cement composites. With its distinguished international team of contributors, Durability of concrete and cement composites is a standard reference for all those concerned with improving the service life of structures using these materials. Analyses a range of materials such as reinforced steel in concrete, pre-stressed concrete and cement composites Discusses key degradation phenomena such as cracking processes and the impact of cold weather conditions A standard reference for those concerned with improving the service life of structures using concrete and cement based composites